Electric cable



1935- I l. 'r. FAUCETT 2,019,297

' ELECTRIC CABLE Filed June 28, 1932 +1 INVENTOR ATTORN EYJT Patented29, 1935 UNITED STATES PATENT ow-101a:

a General Cable corporation, New YorkJl. 1., a corporation of New JerseyThis invention relates to insulated electric cables, and moreparticularly to shielded cables. It is an object of .the invention toprovide improved cable constructions. Other objects and i advantages ofthe invention will appear hereinafter An illustrative embodiment of theinvention selected merely for descriptive purposes is shown in theaccomp nying drawing, in which:

Fig. l is a longitudinal elevation of a single conductor cable withportions of the sheath, shielding layers and insulation removed to.disclose the invention more clearly:

Pig. 2 is an end elevation of the cable shown in Fig. l;

Fig. 3 is a longitudinal elevation of a three conductor cable withportions of the sheath, binding tape, shielding layers and insulationremoved to disclose the invention more clearly; and

Fig. 4 is an end elevation of the cable shown in Fig. 8. L

It has been proposed heretofore to provide one or both surfaces of thewall of insulation surrounding .a cable conductor with a thinelectrostatic shield for purposes of distributing electrical stresswithin the insulation, and limiting the electrical stress to the wall ofinsulation, thereby preventing or reducing ionization at the surface ofthe insulation. l

The electrostatic shield ordinarily takes the form of a metal ribbon ormetallized paper tape helically wound about the conductor before theinsulation is applied, or over the conductor insul'ation, with theadjacent turns of theshielding ribbon or tape lying side by side. Inpractice, adjacent turns of the shielding strip are spaced apartslightLv. It is practically impossible to wind the shielding strip inplace with adjacent edges exactly abutting, and with-a metal ribbon itis desirable to have a slight spacing between adjacent turns to permitbending of the cable with a minimum danger of buckling of the shieldingstrip and damage to the cable insulation.

The shielding layer desirably is very flexible so as to conform closelyto the surface of the insulation at all times. Otherwise spaces would beformed betweenthe shielding layer and the cable insulation when thecable is handled, and such spaces would be under electrical stressduring operation of the cable. Ionization in these spaces would injurethe cable insulation and eventually might result in breakdown of thecable.

In the known constructions the shielding is not perfect because smallionizable spaces are present between adjacent turns of the shieldingstrip June 38, 1m, Serial No. 619,80 1 Claim. (01. 173-266) where theturns lie side by side, and at the inneredgeoftheshieldingstripiftheadjacentturns are overlapped. These spacesordinarily .are very small, but it has been found that the dielectricstrength of an insulated cable is subs stantialiy increased if theseunshielded spaces are eliminated or reduced in size.

According to this invention insulated cable-constructions are providedin which one or both surfaces of the -isulating wall surrounding thecable conductor may be completely shielded, and in which ionizablespaces at the surfaces of the conductor insulation are reduced to aminimum.

Referring first to Figs. 1 and 2, there is shown by way of illustrationa single conductor cable in which both the inner and outer surfaces ofthe insulating wall are shielded. The conductor II is a strandedconductor, and it will be seen from Fig. 2 that small valleys I! existon the outer surface of the conductor between adjacent conductan ingstrands. If the insulating wall were applied immediately over thestranded conductor, these small spaces l2 would be under electricalstress when the cable is in operation.

In accordance with this invention the spaces i2 are shielded by wrappinghelically about the conductor a conducting ribbon ll whose adjacentturns lie side by side, and simultaneously therewith an overlappingconducting tape Ii. This ribbon it should have a fairly high tensile 80strength, and desirably is-a thin metal tape, conveniently copper.Desirably the metal ribbon is perforated as at it to reduce electricallosses due to currents induced therein. It will be apparent that thehelically wound ribbon ll shields to a large extent the spaces l2, butthat if it were not for the overlapping conducting tape I! there wouldbe unshielded spaces between I adjacent turns of the ribbon.

The ribbon II is substantially incompressible, and is fairly still, sothat if adjacent turns were overlapped to eliminate the spaces betweenturns the flexibility of the cable would be lessened, and there would bea small unshielded helically extending space adjacent the overlappingedge of the ribbon, which space wouldnot be completely filled byinsulation applied over the shielding layer. Furthermore, in such aconstruction bending of the cable might result in buckling of theshielding strip, which would injure the cable insulation or enlarge theexisting unshielded spaces.

As the metal ribbon It and conducting tape II are helically wrapped onthe conductor, the tape i5 overlaps and extends beyond one edge of thethisinsulationordinarilytakestheiormoi mam plurality of overlying layersof helically paper tape. the adjacent each layer lying side by side.

ordinarilytakestheiormotaleadtube I'igs.3and4 disclosethe/inventionasapplied to three conductor cable. In the illustrativeshowingtheconductorinsulationisshieldedonLvs onitsoutersuriace.Itwillbeobvious thattheinsulatimeouldalsobeshieldedonitsinner-suriaceinthesamemannerasisshownforsingleconductorcable.

Threes'imilarconductorsfl areeachenclosed inawallfloiinsulation.Overeacholthe insulatingwallsilisappliedashieldinglayer the overlappinghelically wrapped metal ribbon 23 and conducting tape 24. The

three insulated and shielded conductorsare cabled together, and thevalleys between the-conductors conveniently are rounded out with filler'material ll. Denrably the insulated conductorsandtheiillersareheldinassembledpositionbymeansoiahelicallywrappedbindingtapefl.

'll'hisbindingtapeconvenientlyisathinsteelor bronze tape, and is appliedsimultaneously with anoverlapping tape ll whichmaybe aninsulating tape.or which may be a fibrous tape treated with conducting material. It thetape 21 is aconducting tape, the electrical resistance betweentheshielding layers overlying each in-vmlatedconductorandthecablesheathllwill bereduced.Overthebindingstrlpllisthe cablesheathll,whichordinarilywouldheoileadoraleadalloyincableoithetypeshown.

gltwillbeapparent'thatthisinveniion provides shieldedcabl'einwhichionimblespaces adiacentthesuriaceot-thecableinsiflationaresubstsntiallyeliminated. rests have shownthst across? cable constructed according tothis invention hli greatly improved dielectric strength as compare tocables heretofore known. In addition to thi improvement in dielectricstrength, such cabin wouldbeexpectedtohaveamuchlongerliie.

The foregoing description of certain speciii' ts oi the invention isillustrative mere ly.andisnotintendedasdeiiningthelimitse the invention.

I claim: 1.Anelectr1ccablecomprising,incombina tion, conductor. a wallof insulation surround ing conductor. an electrostatic shield over lyingthe insulation said shield comprising helically wound metallic ribbonwhose turns an positioned side by side and a relatively more flexi bleiibrous tape treated with conducting mate rial wound on simultaneouslywith said metallt ribbmsothataturnoitheflbroustapeunderliesoneturnottheribbonandoverliesanadiacentturnoitherlbbomandasheathenclosim v the insulated'conductor.

2.Anelectrlccable,incombina tion, a conductor. a wall 0! insulationsurround ing the conductor, an electrostatic shield inter posed betweenthe conductor and the insulationsaidshieldcomprisingahelicallywoundmetalli ribbon whose turns arepositioned side by aid and a relatively more fleaible nbrous tapetreate1 with conducting material wound on simultane ously with saidmetallic ribbon so that a turi oi the fibrous tape underlies one turn ofthe rib bonanddverliesanadiacentturnottheribbon and a sheath enclosingthe insulated conductor .3. An electric cable comprising", in combination, a conductor. a wall of insulation surround ing the conductor, anelectrostatic shield imme diatelyaddacentonesuriaceotthewalloiinsulation. said shield comprising a metallic ribboi q and a relatively moreflexible fibrous tape treat ed with conducting material helically woundto gether with the tape interlocked with the rib bon in-lappingrelation, and a sheath enclosim the insulated conductor;

4.Anelectric cablecomprising,incombina tion.aconductor.awallotinsuiationsurround ing the conductor, a sheath enclosing the insulated conductor. and an electrostatic shield im mediately adiacent onesurface oi the insulatim wall, said shield comprising a helically wounimetallic ribbon, the turns of which are positione side by side, and ahelically wound. metallize fibrous tape, said metallised fibrous vtapebeim more flexible than the metallic ribbon and eacl turn of the tapeoverlying one turn of the ribboi and underlying an adjacent turn oi! theribbon 5. An electric cable comprising,- in combina tion, a conductor, awall of insulation surround ing the conductor, a sheath enclosing theinsu lated conductor, and an electrostatic shield im mediately adjacentone surface of the insulatim wall, said shield comprising a helicallywoum metallic ribbon, the turns of which are positionei side by side,and a helically wound, metallizel fibrous tape more flexible than themetallic rib hon wound on simultaneously with the ribbon said tape beinginterlocked with the ribbon am extending transversely beyond onelongitudina edge of the ribbon to overlap an adiaceht tun oi the ribbon.K I

6. An electric cable comprising, in combination, a conductor, a wall ofinsulation surrounding the conductor. a sheath enclosing the insulatedconductor. and an electrostatic shield im:medistelyadiacentonesuriaceoitheinsulatim wail, said shield comprising ametal ribbon and a relatively more flexible metallized fibrous tapeaelically wrapped about the conductor with 2. :um 01 the metallizedfibrous tape underlying me turn of the metal ribbon and overlying an ad-Iacent turn of the metal ribbon.

7. An electric cable comprising, in combinaiioni ahcbnductor, a wall ofinsulation surroundng the conductor, a sheath enclosing the insuatedconductor, and an electrostatic shield immediately adjacent one surfaceof the insulating wall, said shield comprising two conducting strips,one 01' which is relatively stiiI and the other of which is relativeLvmore flexible, simultaneously helically wound about the conductor withthe turns oi. the relatively stifl' strip side by side and with theturns of the more flexible strip extending between and underlying andoverlying adjacent turns 01' the relatively stifl. strip.

IRVING T. FAUCE'IT.

